This invention relates to a screw with a threaded shaft which has a slot running longitudinally which divides the threaded shaft into two halves.
A screw is known from DE 38 12 111 C2 corresponding to U.S. Pat. No. 4,822,225 which can be inserted especially quickly into a threaded hole or application-related cored hole because it does not have to be threaded into it at the beginning, but needs merely to be pushed into it axially at first, letting the threads of the screw slip over the threads of the hole. When screws of the above kind are used at places where vibration and oscillation occur there is the danger of accidental loosening of the screws in the course of time. It is, therefore, necessary to secure the screws against unintended loosening.
Very different means are known for securing screws. It is common, for example, to slip a spring or lock washer onto the threaded shaft to produce a bias force on the screw head when the screw is tightened. Another common method of screw locking consists in binding the screw head to the surface with a lacquer against which it presses when the screw is tightened. The known screw locks involve relatively great additional work, so that for cost reasons such screw locks are not applied and instead the risk of unintentional loosening of the screws is accepted.
This invention is addressed to the problem of designing a screw of the kind described above such that it can be secured against unintentional loosening with as little work as possible. This problem is solved by the invention by the fact that a plastic mass filling the slot partially or entirely is provided in the slot.
Such a screw is only slightly more expensive than a screw unsecured against unintentional loosening. Therefore one can use such screws with locking means at basically little additional cost and thus prevent unintentional loosening of the screws. Since the mass according to the invention is plastic it does not interfere with the drawing together of the shaft halves when the threaded shaft is pressed axially into a threaded hole. The screw according to the invention can therefore be inserted at first axially into a threaded hole while the mass is compressed in its slot.
It is especially desirable if, according to an advantageous embodiment of the invention, the mass is an elastic polymer. Such a mass is especially cheap and brings about an effective screw lock.
To further increase the holding power of the screw lock it is helpful if, according to another embodiment of the invention, the mass is a fiber material or synthetic material mixed with fibers or a composite material of synthetic material and metal.
The force involved in inserting the screw is especially low if the mass is a synthetic material mass, such as a lacquer, which hardens under pressure.
Since when the screw is inserted into a threaded hole the shaft halves are forced together from both sides of the slot, the mass in the slot can pass out of it upon insertion so as to exercise the locking function, so that it does not interfere with insertion if the mass reaches no further than the outer contour of the threaded shaft.
If especially great locking forces are required, however, provision can be made for the mass to protrude on both sides of the slot beyond the contour of the outside diameter of the threaded shaft.
The mass can be reliably anchored in the slot if the screw shaft has at least one transverse bore leading into the slot and the mass reaches into this transverse bore.
It contributes to a further increase of the holding power if the mass at the same time coats at least a portion of the circumferential surface of the threaded shaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.